What this method is

Wemmerlöv PPB + LALB is a fast ULS heuristic in the Look-ahead / look-back family. It constructs a feasible replenishment plan without claiming an optimality proof. Use it only when the documented applicability conditions match the instance.

Core idea

The method scans the planning horizon and constructs replenishment cycles according to its published decision rule. The library then reconstructs production, inventory, setups and cost components through the common heuristic solution builder.

using ULSAlgorithms.Abstractions;
using ULSAlgorithms.Models;
using ULSAlgorithms.Heuristics;

var problem = new UlsProblem(
    demands:             [20.0, 30.0, 25.0, 40.0],
    setupCosts:          [200.0, 200.0, 200.0, 200.0],
    unitProductionCosts: [0.0, 0.0, 0.0, 0.0],
    holdingCosts:        [4.0, 4.0, 4.0, 0.0]);

IUlsSolver solver = new WemmerlovPpbLookAheadLookBackSolver();
var result = solver.Solve(problem);

Console.WriteLine(result.Status);
Console.WriteLine(result.ObjectiveValue);

The input example intentionally uses stationary, positive-demand data so it is compatible with restricted methods too. Always check the applicability box for your own instance.

Reference & provenance

Wemmerlöv (1983), The Part-Period Balancing Algorithm and Its Look Ahead-Look Back Feature: A Theoretical and Experimental Analysis of a Single Stage Lot-Sizing Procedure, Journal of Operations Management 4(1), 23-39 · DOI 10.1016/0272-6963(83)90023-2